Semiconductor memory devices are separated into volatile memory devices and nonvolatile memory devices. Read and write speeds of the volatile memory devices are fast, but they lose contents stored therein at power-off. In contrast, nonvolatile memory devices retain contents stored therein even at power-off. Thus, nonvolatile memory devices are used to store contents that must be retained regardless of whether a power is supplied. In particular, among nonvolatile memory devices, a flash memory device is advantageous to an appliance to an auxiliary mass storage device in that it is highly integrated in relation to a conventional EEPROM.
With advances in the technology and lowering of prices of the flash memory device, the flash memory device is being used as a storage medium for replacing a hard disk drive (HDD). A storage device using the flash memory device may have been fabricated in various ways. Such a storage device may be used as a solid state drive (SSD), an SD card, and so on. The storage device contains a controller to control the flash memory device.
The flash memory device has been fabricated by a fine process technology to increase a degree of integration. In the flash memory device, a space between word lines may decrease in proportion to an increase in the degree of integration. Thus, as well as fail-out of the flash memory device, runtime failure may increase.